1. Field of the Invention
The present invention relates to a helical compression spring for use in a strut type vehicle suspension, and relates to a strut type vehicle suspension having a helical compression spring.
2. Description of the Related Arts
In general, a vehicle suspension is provided with a helical compression spring, which is generally designed to provide a coil axis that coincides with a direction of reaction force of the spring. Various types of vehicle suspension system have been known heretofore. Among them, a strut type suspension with a shock absorber employed as a strut for positioning a wheel is popular. According to the strut type suspension, however, due to a displacement between its load input axis and strut axis, a bending moment is exerted on the strut, with side force acting on a guide and a piston of the strut. This side force prevents the piston from sliding smoothly in the guide to act as the shock absorber. In order to compensate the bending moment, it has been known to arrange a coil axis of a cylindrical helical compression spring to be offset to the strut axis.
Since the arrangement between the coil axis of the helical compression spring and the strut axis of the shock absorber is determined geometrically, it has been required that the helical compression spring should be designed to coincide its coil axis with the direction of reaction force of the spring. In order to meet such requirement, various studies have been made, including the article xe2x80x9cApproaches to Minimizing Side Force of Helical Coil Springs in Suspension Designxe2x80x9d, presented by engineers including the inventor of the present application, and received by Japan Society for Spring Research on Aug. 28, 1995, wherein it was proposed to minimize the side force of the helical compression spring.
In contrast, on pages 56 and 57 of xe2x80x9cAutomotive Engineeringxe2x80x9d issued on September 1997, there are disclosed two kinds of spring having a coil axis inclined to an axis of a shock absorber so as to minimize a friction of the shock absorber for a strut type suspension. One spring is so constituted that one end coil is formed into a pig tail coil, and an axis for connecting the center of the pig tail coil and the center of the other end coil is served as the axis of the shock absorber, and that the axis and a spring force direction (reaction force direction) are arranged to provide a certain angle so that they are intersected at the center of the other end coil. The other spring is so constituted that both end coils are formed into the pig tail coils, and an axis for connecting the centers of those end coils is served as the axis of the shock absorber, and that the axis and the spring force direction are arranged to provide a certain angle so that they are intersected at a longitudinal center of the spring.
With respect to the vehicle suspension, further reduction in size is required now. By means of mere improvement made to a supporting mechanism of the strut having a conventional cylindrical helical compression spring, therefore, it is difficult to compensate the bending moment exerted on the strut due to load from a road. Rather, it is necessary to positively increase a side force applied by the helical compression spring to the strut type suspension. However, it is not easy to apply a desired side force to the suspension by the conventional helical compression spring. By means of the helical spring disclosed in the aforementioned publication of the Automotive Engineering, sufficient side force necessary for the strut type suspension can not be obtained. Namely, it is impossible to apply the side force to the guide portion and piston portion of the strut enough to compensate the side force exerted thereon.
Accordingly, it is an object of the present invention to provide a helical compression spring for a strut type suspension with a simple structure to apply a desired side force to the strut when mounted on the strut type suspension.
Another object of the present invention is to provide a strut type vehicle suspension for applying a desired side force to a strut of the suspension.
In accomplishing the above and other objects of the present application, a helical compression spring for a vehicle suspension according to the present invention is compressed between an upper seat and a lower seat. The spring is formed to provide an end coil center line connecting the centers of an upper end coil and a lower end coil of the spring to be offset to a coil axis of a body portion of the spring. A pitch of the lower end coil is set to tilt a lower end plane of the spring seated on the lower seat at a first predetermined angle to the lower seat in a direction for shortening the longitudinal length of one side of the spring closer to the end coil center line than the coil axis, in an unloaded state of the spring, and/or a pitch of the upper end coil is set to tilt an upper end plane of the spring seated on the upper seat at a second predetermined angle in a direction for shortening the longitudinal length of the other side of the spring closer to the coil axis than the end coil center line, in the unloaded state of the spring.
Preferably, the upper end coil and the lower end coil are formed in a pig tail configuration, respectively.
A strut type vehicle suspension according to the present invention includes a strut mounted at the upper end thereof on a vehicle body for supporting a wheel, a lower seat fixed to the strut, an upper seat mounted on the vehicle body, and a helical compression spring mounted between the lower seat and the upper seat, with the strut enclosed in the spring. The helical spring is preferably formed to provide an end coil center line connecting the centers of an upper end coil and a lower end coil of the spring to be offset to a coil axis of a body portion of the spring. The lower seat is fixed to the strut to tilt the lower seat at a first predetermined angle in a direction for shortening the longitudinal length of one side of the spring closer to the coil axis than the end coil center line, and/or the upper seat is mounted on the vehicle body to tilt the upper seat at a second predetermined angle in a direction for shortening the longitudinal length of the other side of the spring closer to the end coil center line than the coil axis. And, the spring is held in such a state that the other side of the spring closer to the end coil center line than the coil axis is positioned at the inside of the vehicle body.
In the strut type vehicle suspension as described above, the upper end coil and the lower end coil of the spring may be formed in a pig tail configuration, respectively.